T cell activation is the result of the integration of signals across the T cell receptor and adjacent co-receptors. The signaling lymphocyte activation molecules (SLAM) family are transmembrane co-receptors that modulate antigen driven T cell responses. Signal transduction downstream of the SLAM receptor is mediated by the adaptor protein SLAM Associated Protein (SAP), a small intracellular protein with a single SH2 binding domain that can recruit tyrosine kinases as well as shield phosphorylated sites from dephosphorylation. Balanced SLAM-SAP signaling within T cells is required for healthy immunity, with deficiency or overexpression prompting autoimmune diseases. Better understanding of the molecular pathways involved in the intracellular signaling downstream of SLAM could provide treatment targets for these autoimmune diseases.

Background: Endomyocardial biopsy (EMB) is considered the gold standard for diagnosing myocardial involvement in most inflammatory conditions, including systemic lupus erythematosus (SLE). However, EMBs are rarely performed, and most of the myocardial histopathology reports in SLE consist of postmortem data. We therefore sought to describe the histopathologic findings of contemporary EMBs in SLE performed in clinical practice. Methods: A retrospective review of histopathology reports from SLE patients who underwent EMB from 1994 to 2017 was performed. A total of 41 SLE patients had cardiac pathology reports. Of these, 11 histopathology reports were EMBs, and the remaining were valvular specimens. Results: A total of 11 SLE EMBs were reviewed. It was found that 45% of the patients had hypertension, 27% had coronary artery disease, 9% had hyperlipidemia, and 36% had end-stage renal disease. None had diabetes or smoked. The mean left ventricular ejection fraction was 37%. On histopathology, 10 had mild interstitial fibrosis, 9 had myocyte hypertrophy, 3 had organized blood clots, and 3 had a mild infiltration of lymphocytes and macrophages without clear evidence of myocarditis. None had vasculitis, endocarditis, ischemia, amyloid deposition, or lamellar or curvilinear inclusions. Conclusion: EMBs are rarely performed in SLE. In this case series, nonspecific interstitial fibrosis and myocyte hypertrophy were the most common findings, suggesting EMBs have limited value in the diagnosis of cardiac involvement in SLE and rather rule out competing conditions. These data support the need for diagnostic methods with high sensitivity and specificity for SLE heart disease.

Signaling lymphocyte activation molecule family member 6 (SLAMF6) is a T cell co-receptor. Previously, we showed that SLAMF6 clustering was required for T cell activation. To better understand the relationship between SLAMF6 location and function and to evaluate the role of SLAMF6 as a therapeutic target, we investigated how its compartmentalization on the cell surface affects T cell functions. We used biochemical and co-culture assays to show that T cell activity is enhanced when SLAMF6 colocalizes with the CD3 complex. Mechanistically, co-immunoprecipitation analysis revealed the SLAMF6-interacting proteins to be those essential for signaling downstream of T cell receptor, suggesting the two receptors share downstream signaling pathways. Bispecific anti-CD3/SLAMF6 antibodies, designed to promote SLAMF6 clustering with CD3, enhanced T cell activation. Meanwhile, anti-CD45/SLAMF6 antibodies inhibited SLAMF6 clustering with T cell receptor, likely because of the steric hindrance, but nevertheless enhanced T cell activation. We conclude that SLAMF6 bispecific antibodies have a role in modulating T cell responses, and future work will evaluate the therapeutic potential in tumor models.

Objective: Immune checkpoint inhibitors (ICIs) have significantly advanced cancer treatment, but they can also lead to immune-related adverse events (irAEs), including inflammatory arthritis. Understanding the risk factors and underlying mechanisms of irAE pathogenesis is crucial for optimal patient management. Increasing evidence suggests that ICI-mediated activation of tissue-resident memory T cells (T _RM ) significantly eliminates cancer cells and is associated with irAE-related colitis and dermatitis. However, it remains unknown why the development of these irAEs is restricted to a subset of patients. We hypothesized that osteoarthritis (OA) associated tissue damage and chronic inflammation lead to the recruitment and differentiation of joint T _RM cells, predisposing individuals to ICI-induced arthritis. Methods: Using a comprehensive approach, we compared the prevalence of OA in patients with irAE-arthritis to those with irAE non-arthritis and those without irAEs. Additionally, we used advanced immunophenotyping techniques to characterize T-cell populations in the blood and synovial fluid of patients with OA and irAE-arthritis. Results: Our findings revealed a significantly higher prevalence of OA in patients who developed irAE-arthritis than controls. Furthermore, the multivariable analysis identified OA, body mass index, and smoking as independent risk factors for the development of irAE-arthritis. T _RM cells expressing programmed cell death protein-1 (PD-1) were the predominant synovial T cells in OA joints. These cells were directly targeted by ICIs, resulting in an inflammatory immune response and the transition from OA to irAE-arthritis. Conclusion: This study, the first of its kind, identifies OA as a significant risk factor for irAEarthritis. It reveals a potential mechanism by which ICIs activate PD-1-positive T _RM cells in OA joints, resulting in tissue inflammation and irAE-arthritis. This research could significantly enhance the management and treatment of patients with cancer receiving ICIs.